(1) Field of the Invention
The present invention relates to acoustically activated switches and, more particularly, to an acoustically activated switch with frequency band limiting that serves as an adapter to interconnect a single input device with multiple transducers each producing a non-synchronized signal, and with the adapter providing an output representative of the first to be received signal generated by the multiple transducers.
(2) Description of the Prior Art
Acoustic switches activated by audible sound are known and serve a variety of functions, such as those being used at sea and which are interconnected to transducers, such as hydrophones located on the port and starboard sides of the ships. Devices that respond to signals received from transponder are known and some of which are disclosed in U.S. Pat. Nos. 3,320,576; 4,604,738, and 5,341,347.
At-sea systems may advantageously employ communication modulation techniques, such as a frequency-shift keying (FSK) technique that shifts a carrier frequency over a range of a few hundred hertz. The FSK technique provides modulation that merges binary data into the carrier and creates only two changes in frequency; one for a logic xe2x80x9c0xe2x80x9d, another for a logic xe2x80x9c1xe2x80x9d. For such at-sea systems for certain applications, it is important that the at-sea system respond to the input from the hydrophone that provides the highest level of signal. The signal at the highest level is most likely generated by the hydrophone located nearest the at-sea system. Furthermore, it is important that the signals from the hydrophones not be intermingled with each other, which would otherwise lead to corruption of the associated signals resulting in a possible unrecognizable bit pattern. All of these possible drawbacks may occur for a system having a single channel input, but required to accept input signals generated from multiple transducers.
It is desired that a acoustic switch be provided that interconnects multiple transducers, each receiving an (FSK) signal, to a single channel device and ensures that the signal from the transducer closest to a at-sea system is supplied to the single channel device and also that the FSK signals from the multiple transducers are not mixed, which would otherwise result in a possible unrecognizable bit pattern.
Accordingly, it is a general purpose and object of the present invention to provide for an acoustically activated switch that allows for a single input channel device to receive acoustic signals, particularly FSK signals, from multiple transducers. It is a further object to provide an acoustic switch that ensures that the signal from the transducer closest to the single channel device is supplied to the single channel input device. Further, it is an object of the present invention to ensure that received signals from the multiple transducers generating FSK signals are not intermingled or mixed, and thus preventing unrecognizable bit patterns.
The present invention provides an acoustic switch serving as an adapter for handling signals from at least two transponders and determines which of the transponders is closest to the adapter. The adapter comprises at least first and second band pass filters for respectively receiving an input signal generated from at least first and second transponders. The first and second band pass filters generate respective filtered A.C. output signals. The adapter further comprises at least first and second full wave rectifiers respectively receiving the filtered A.C. output signals and respectively generating representative D.C. output signals. In addition, the adapter comprises at least first and second level detectors respectively receiving the D.C. output signals and respectively generating an output signal when the level of the received D.C. output signal is greater than a predetermined threshold. The adapter further comprises a threshold detector receiving the output signals of god the first and second level detectors. The adapter further comprises an output driver receiving the output signal of the threshold detector and the output signals of the first and second band pass filters. The output driver generates an output signal derived from the transponder closest to the adapter.